The present invention relates to an automatic transmission having a plurality of ranges manually selectable by a driver, and more particularly to an apparatus for detecting in which one of the plurality of ranges the automatic transmission is placed.
In order to control an automatic transmission, it is the common practice to detect in which one of a plurality of manually selected ranges the automatic transmission is placed. Service manual "NISSAN FULL-RANGE ELECTRONICALLY CONTROLLED AUTOMATIC TRANSMISSION E-AT, RE4R01A TYPE" (A261C07) was issued by Nissan Motor Co., Ltd. in Mar., 1987. According to this publication, an automatic transmission of the RE4R01A type is described and known. This known automatic transmission has six manually selectable ranges, namely, P (parking), R (reverse), N (neutral), D (drive), 2 (second), and 1 (first) ranges. As shown in page II-3 of the publication, the automatic transmission has a select range lever which is operatively connected to a manual valve of a hydraulic control circuit (see pages I-56 to I-66 of the publication) and linked to a manual control lever (see page I-88 of the publication) disposed near a driver's seat. The select range lever is moveable to select one of the six range positions. In order to detect in which one of the six ranges the automatic transmission is placed, a so-called inhibitor switch is installed near the select range lever (see page II-3 of the publication). In order to transmit information from the inhibitor switch to an A/T (automatic transmission) control unit (see page I-6 of the publication), six signal lines extend from the inhibitor switch to the A/T control unit. The inhibitor switch comprises a contact support, in the form of a fixed plate, fixedly mounted to the transmission body, a cooperating moveable contact moveable by the select range lever to assume six positions, namely P (parking), R (reverse), N (neutral), D (drive), 2 (second), and 1 (first) positions. Arranged on the contact support are a common stationary contact cooperating with the moveable contact, six individual stationary contacts, and two pairs of normally open contacts. When the moveable contact assumes the P position, one of the two pairs of normally open contacts is closed to allow electric current to pass through a stator motor, and when it assumes the N position, the other of the two pairs of normally open contacts is closed to allow electric current to pass through the stator motor. The six individual stationary contacts are arranged in the six positions, respectively. When the P position, the moveable contact bridges a first one of the individual stationary contacts with the common contact. At the R position, the moveable contact bridges a second one of the individual stationary contacts with the common contact, turning on reverse lamps. At the N position, the moveable contact bridges a third one of the individual stationary contacts with the common contact. At the D position, the moveable contact bridges a fourth one of the individual stationary contacts with the common contact. At the 2 position, the moveable contact bridges a fifth one of the individual stationary contacts with the common contact. At the 1 position, the moveable contact bridges a sixth one of the individual stationary contacts with the common contact. Six signal lines are electrically connected to the six individual stationary contacts, respectively. In order to decide which one of the six positions the moveable contact assumes, the A/T control unit determines which one of the six signal lines is conductive. More specifically, if one of the six signal lines is conductive, and the other five signal lines are non-conductive, it is determined that the moveable contact assumed the corresponding one of the six positions with the individual contact having a conductive signal line.
In addition to the above-mentioned six signal lines connected to the six individual stationary contacts, a seventh signal line is connected to the common contact. Thus, seven signal lines are necessary to detect six ranges selectable in the automatic transmission. In other words, N+1 signal lines are necessary for detecting N ranges selectable in the automatic transmission.
This known apparatus poses a problem that a harness of signal lines becomes thick and thus inflexible. This makes it physically difficult to arrange the harness and connect the harness with another harness.
An object of the present invention is to improve an apparatus of the above-mentioned type such that detection of a plurality of ranges selected in an automatic transmission is conducted with a fewer number of signal lines.